Diatom Assemblages From Surface Sediments of Two Coastal Lagoons, the Central Part of the Red Sea, Saudi Arabia and Their Associated Environmental Variables

The composition and distribution pattern of diatom assemblages in the surface sediments of Sharm Al-Kharrar and Al-Shuaiba lagoons, situated on the central part of the Red Sea coastline of Saudi Arabia, were analyzed. A total of 191 diatom species from 53 genera were identified. A highly diverse diatom flora dominated by the genera Mastogolia, Amphora sensu lato, Lyrella, and Navicula sensu lato species was observed. Diatom species composition showed the dominance of the benthic forms over the epiphytic and planktonic ones, which can be attributed to the shallowness of the environments. The relationship between the recognized diatom taxa and measured environmental variables was explored using multivariate statistical techniques. Hierarchical ascending clustering and detrended correspondence analyses differentiated six representative diatom assemblages in each Lagoon. Canonical correspondence analysis revealed that grain size, organic matter content, and water depth appeared to be significant environmental factors affecting the distribution and structure of the documented diatom assemblages, while pH, salinity, and temperature were less influential. The majority of species recorded were polyhalobous benthic diatoms, accompanied by a limited abundance of mesohalobous and substantial amounts of oligohalobous forms, which are probably of allochthonous origin and resulting from freshwater input of near seasonal wadi streams and human activities. A comparison between the recognized diatom assemblages and the previously recorded taxa in surrounding areas was made.